/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
/*-------------------------------------------------------------------------
 *
 * jsonb_util.c
 *    converting between Jsonb and JsonbValues, and iterating.
 *
 * Copyright (c) 2014-2015, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/jsonb_util.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/hash.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/jsonb.h"
#include "utils/memutils.h"

/*
 * Maximum number of elements in an array (or key/value pairs in an object).
 * This is limited by two things: the size of the JEntry array must fit
 * in MaxAllocSize, and the number of elements (or pairs) must fit in the bits
 * reserved for that in the JsonbContainer.header field.
 *
 * (The total size of an array's or object's elements is also limited by
 * JENTRY_OFFLENMASK, but we're not concerned about that here.)
 */
#define JSONB_MAX_ELEMS (Min(MaxAllocSize / sizeof(JsonbValue), JB_CMASK))
#define JSONB_MAX_PAIRS (Min(MaxAllocSize / sizeof(JsonbPair), JB_CMASK))

static void fillJsonbValue(JsonbContainer *container, int index,
         char *base_addr, uint32 offset,
         JsonbValue *result);
static bool equalsJsonbScalarValue(JsonbValue *a, JsonbValue *b);
static int  compareJsonbScalarValue(JsonbValue *a, JsonbValue *b);
static Jsonb *convertToJsonb(JsonbValue *val);
static void convertJsonbValue(StringInfo buffer, JEntry *header, JsonbValue *val, int level);
static void convertJsonbArray(StringInfo buffer, JEntry *header, JsonbValue *val, int level);
static void convertJsonbObject(StringInfo buffer, JEntry *header, JsonbValue *val, int level);
static void convertJsonbScalar(StringInfo buffer, JEntry *header, JsonbValue *scalarVal);

static int  reserveFromBuffer(StringInfo buffer, int len);
static void appendToBuffer(StringInfo buffer, const char *data, int len);
static void copyToBuffer(StringInfo buffer, int offset, const char *data, int len);
static short padBufferToInt(StringInfo buffer);

static JsonbIterator *iteratorFromContainer(JsonbContainer *container, JsonbIterator *parent);
static JsonbIterator *freeAndGetParent(JsonbIterator *it);
static JsonbParseState *pushState(JsonbParseState **pstate);
static void appendKey(JsonbParseState *pstate, JsonbValue *scalarVal);
static void appendValue(JsonbParseState *pstate, JsonbValue *scalarVal);
static void appendElement(JsonbParseState *pstate, JsonbValue *scalarVal);
static int  lengthCompareJsonbStringValue(const void *a, const void *b);
static int  lengthCompareJsonbPair(const void *a, const void *b, void *arg);
static void uniqueifyJsonbObject(JsonbValue *object);
static JsonbValue *pushJsonbValueScalar(JsonbParseState **pstate,
           JsonbIteratorToken seq,
           JsonbValue *scalarVal);

/*
 * Turn an in-memory JsonbValue into a Jsonb for on-disk storage.
 *
 * There isn't a JsonbToJsonbValue(), because generally we find it more
 * convenient to directly iterate through the Jsonb representation and only
 * really convert nested scalar values.  JsonbIteratorNext() does this, so that
 * clients of the iteration code don't have to directly deal with the binary
 * representation (JsonbDeepContains() is a notable exception, although all
 * exceptions are internal to this module).  In general, functions that accept
 * a JsonbValue argument are concerned with the manipulation of scalar values,
 * or simple containers of scalar values, where it would be inconvenient to
 * deal with a great amount of other state.
 */
Jsonb *
JsonbValueToJsonb(JsonbValue *val)
{
  Jsonb    *out;

  if (IsAJsonbScalar(val))
  {
    /* Scalar value */
    JsonbParseState *pstate = NULL;
    JsonbValue *res;
    JsonbValue  scalarArray;

    scalarArray.type = jbvArray;
    scalarArray.val.array.rawScalar = true;
    scalarArray.val.array.nElems = 1;

    pushJsonbValue(&pstate, WJB_BEGIN_ARRAY, &scalarArray);
    pushJsonbValue(&pstate, WJB_ELEM, val);
    res = pushJsonbValue(&pstate, WJB_END_ARRAY, NULL);

    out = convertToJsonb(res);
  }
  else if (val->type == jbvObject || val->type == jbvArray)
  {
    out = convertToJsonb(val);
  }
  else
  {
    Assert(val->type == jbvBinary);
    out = palloc(VARHDRSZ + val->val.binary.len);
    SET_VARSIZE(out, VARHDRSZ + val->val.binary.len);
    memcpy(VARDATA(out), val->val.binary.data, val->val.binary.len);
  }

  return out;
}

/*
 * Get the offset of the variable-length portion of a Jsonb node within
 * the variable-length-data part of its container.  The node is identified
 * by index within the container's JEntry array.
 */
uint32
getJsonbOffset(const JsonbContainer *jc, int index)
{
  uint32    offset = 0;
  int     i;

  /*
   * Start offset of this entry is equal to the end offset of the previous
   * entry.  Walk backwards to the most recent entry stored as an end
   * offset, returning that offset plus any lengths in between.
   */
  for (i = index - 1; i >= 0; i--)
  {
    offset += JBE_OFFLENFLD(jc->children[i]);
    if (JBE_HAS_OFF(jc->children[i]))
      break;
  }

  return offset;
}

/*
 * Get the length of the variable-length portion of a Jsonb node.
 * The node is identified by index within the container's JEntry array.
 */
uint32
getJsonbLength(const JsonbContainer *jc, int index)
{
  uint32    off;
  uint32    len;

  /*
   * If the length is stored directly in the JEntry, just return it.
   * Otherwise, get the begin offset of the entry, and subtract that from
   * the stored end+1 offset.
   */
  if (JBE_HAS_OFF(jc->children[index]))
  {
    off = getJsonbOffset(jc, index);
    len = JBE_OFFLENFLD(jc->children[index]) - off;
  }
  else
    len = JBE_OFFLENFLD(jc->children[index]);

  return len;
}

/*
 * BT comparator worker function.  Returns an integer less than, equal to, or
 * greater than zero, indicating whether a is less than, equal to, or greater
 * than b.  Consistent with the requirements for a B-Tree operator class
 *
 * Strings are compared lexically, in contrast with other places where we use a
 * much simpler comparator logic for searching through Strings.  Since this is
 * called from B-Tree support function 1, we're careful about not leaking
 * memory here.
 */
int
compareJsonbContainers(JsonbContainer *a, JsonbContainer *b)
{
  JsonbIterator *ita,
         *itb;
  int     res = 0;

  ita = JsonbIteratorInit(a);
  itb = JsonbIteratorInit(b);

  do
  {
    JsonbValue  va,
          vb;
    JsonbIteratorToken ra,
          rb;

    ra = JsonbIteratorNext(&ita, &va, false);
    rb = JsonbIteratorNext(&itb, &vb, false);

    if (ra == rb)
    {
      if (ra == WJB_DONE)
      {
        /* Decisively equal */
        break;
      }

      if (ra == WJB_END_ARRAY || ra == WJB_END_OBJECT)
      {
        /*
         * There is no array or object to compare at this stage of
         * processing.  jbvArray/jbvObject values are compared
         * initially, at the WJB_BEGIN_ARRAY and WJB_BEGIN_OBJECT
         * tokens.
         */
        continue;
      }

      if (va.type == vb.type)
      {
        switch (va.type)
        {
          case jbvString:
          case jbvNull:
          case jbvNumeric:
          case jbvBool:
            res = compareJsonbScalarValue(&va, &vb);
            break;
          case jbvArray:

            /*
             * This could be a "raw scalar" pseudo array.  That's
             * a special case here though, since we still want the
             * general type-based comparisons to apply, and as far
             * as we're concerned a pseudo array is just a scalar.
             */
            if (va.val.array.rawScalar != vb.val.array.rawScalar)
              res = (va.val.array.rawScalar) ? -1 : 1;
            if (va.val.array.nElems != vb.val.array.nElems)
              res = (va.val.array.nElems > vb.val.array.nElems) ? 1 : -1;
            break;
          case jbvObject:
            if (va.val.object.nPairs != vb.val.object.nPairs)
              res = (va.val.object.nPairs > vb.val.object.nPairs) ? 1 : -1;
            break;
          case jbvBinary:
            elog(ERROR, "unexpected jbvBinary value");
        }
      }
      else
      {
        /* Type-defined order */
        res = (va.type > vb.type) ? 1 : -1;
      }
    }
    else
    {
      /*
       * It's safe to assume that the types differed, and that the va
       * and vb values passed were set.
       *
       * If the two values were of the same container type, then there'd
       * have been a chance to observe the variation in the number of
       * elements/pairs (when processing WJB_BEGIN_OBJECT, say). They're
       * either two heterogeneously-typed containers, or a container and
       * some scalar type.
       *
       * We don't have to consider the WJB_END_ARRAY and WJB_END_OBJECT
       * cases here, because we would have seen the corresponding
       * WJB_BEGIN_ARRAY and WJB_BEGIN_OBJECT tokens first, and
       * concluded that they don't match.
       */
      Assert(ra != WJB_END_ARRAY && ra != WJB_END_OBJECT);
      Assert(rb != WJB_END_ARRAY && rb != WJB_END_OBJECT);

      Assert(va.type != vb.type);
      Assert(va.type != jbvBinary);
      Assert(vb.type != jbvBinary);
      /* Type-defined order */
      res = (va.type > vb.type) ? 1 : -1;
    }
  }
  while (res == 0);

  while (ita != NULL)
  {
    JsonbIterator *i = ita->parent;

    pfree(ita);
    ita = i;
  }
  while (itb != NULL)
  {
    JsonbIterator *i = itb->parent;

    pfree(itb);
    itb = i;
  }

  return res;
}

/*
 * Find value in object (i.e. the "value" part of some key/value pair in an
 * object), or find a matching element if we're looking through an array.  Do
 * so on the basis of equality of the object keys only, or alternatively
 * element values only, with a caller-supplied value "key".  The "flags"
 * argument allows the caller to specify which container types are of interest.
 *
 * This exported utility function exists to facilitate various cases concerned
 * with "containment".  If asked to look through an object, the caller had
 * better pass a Jsonb String, because their keys can only be strings.
 * Otherwise, for an array, any type of JsonbValue will do.
 *
 * In order to proceed with the search, it is necessary for callers to have
 * both specified an interest in exactly one particular container type with an
 * appropriate flag, as well as having the pointed-to Jsonb container be of
 * one of those same container types at the top level. (Actually, we just do
 * whichever makes sense to save callers the trouble of figuring it out - at
 * most one can make sense, because the container either points to an array
 * (possibly a "raw scalar" pseudo array) or an object.)
 *
 * Note that we can return a jbvBinary JsonbValue if this is called on an
 * object, but we never do so on an array.  If the caller asks to look through
 * a container type that is not of the type pointed to by the container,
 * immediately fall through and return NULL.  If we cannot find the value,
 * return NULL.  Otherwise, return palloc()'d copy of value.
 */
JsonbValue *
findJsonbValueFromContainer(JsonbContainer *container, uint32 flags,
              JsonbValue *key)
{
  JEntry     *children = container->children;
  int     count = (container->header & JB_CMASK);
  JsonbValue *result;

  Assert((flags & ~(JB_FARRAY | JB_FOBJECT)) == 0);

  /* Quick out without a palloc cycle if object/array is empty */
  if (count <= 0)
    return NULL;

  result = palloc(sizeof(JsonbValue));

  if (flags & JB_FARRAY & container->header)
  {
    char     *base_addr = (char *) (children + count);
    uint32    offset = 0;
    int     i;

    for (i = 0; i < count; i++)
    {
      fillJsonbValue(container, i, base_addr, offset, result);

      if (key->type == result->type)
      {
        if (equalsJsonbScalarValue(key, result))
          return result;
      }

      JBE_ADVANCE_OFFSET(offset, children[i]);
    }
  }
  else if (flags & JB_FOBJECT & container->header)
  {
    /* Since this is an object, account for *Pairs* of Jentrys */
    char     *base_addr = (char *) (children + count * 2);
    uint32    stopLow = 0,
          stopHigh = count;

    /* Object key passed by caller must be a string */
    Assert(key->type == jbvString);

    /* Binary search on object/pair keys *only* */
    while (stopLow < stopHigh)
    {
      uint32    stopMiddle;
      int     difference;
      JsonbValue  candidate;

      stopMiddle = stopLow + (stopHigh - stopLow) / 2;

      candidate.type = jbvString;
      candidate.val.string.val =
        base_addr + getJsonbOffset(container, stopMiddle);
      candidate.val.string.len = getJsonbLength(container, stopMiddle);

      difference = lengthCompareJsonbStringValue(&candidate, key);

      if (difference == 0)
      {
        /* Found our key, return corresponding value */
        int     index = stopMiddle + count;

        fillJsonbValue(container, index, base_addr,
                 getJsonbOffset(container, index),
                 result);

        return result;
      }
      else
      {
        if (difference < 0)
          stopLow = stopMiddle + 1;
        else
          stopHigh = stopMiddle;
      }
    }
  }

  /* Not found */
  pfree(result);
  return NULL;
}

/*
 * Get i-th value of a Jsonb array.
 *
 * Returns palloc()'d copy of the value, or NULL if it does not exist.
 */
JsonbValue *
getIthJsonbValueFromContainer(JsonbContainer *container, uint32 i)
{
  JsonbValue *result;
  char     *base_addr;
  uint32    nelements;

  if ((container->header & JB_FARRAY) == 0)
    elog(ERROR, "not a jsonb array");

  nelements = container->header & JB_CMASK;
  base_addr = (char *) &container->children[nelements];

  if (i >= nelements)
    return NULL;

  result = palloc(sizeof(JsonbValue));

  fillJsonbValue(container, i, base_addr,
           getJsonbOffset(container, i),
           result);

  return result;
}

/*
 * A helper function to fill in a JsonbValue to represent an element of an
 * array, or a key or value of an object.
 *
 * The node's JEntry is at container->children[index], and its variable-length
 * data is at base_addr + offset.  We make the caller determine the offset
 * since in many cases the caller can amortize that work across multiple
 * children.  When it can't, it can just call getJsonbOffset().
 *
 * A nested array or object will be returned as jbvBinary, ie. it won't be
 * expanded.
 */
static void
fillJsonbValue(JsonbContainer *container, int index,
         char *base_addr, uint32 offset,
         JsonbValue *result)
{
  JEntry    entry = container->children[index];

  if (JBE_ISNULL(entry))
  {
    result->type = jbvNull;
  }
  else if (JBE_ISSTRING(entry))
  {
    result->type = jbvString;
    result->val.string.val = base_addr + offset;
    result->val.string.len = getJsonbLength(container, index);
    Assert(result->val.string.len >= 0);
  }
  else if (JBE_ISNUMERIC(entry))
  {
    result->type = jbvNumeric;
    result->val.numeric = (Numeric) (base_addr + INTALIGN(offset));
  }
  else if (JBE_ISBOOL_TRUE(entry))
  {
    result->type = jbvBool;
    result->val.boolean = true;
  }
  else if (JBE_ISBOOL_FALSE(entry))
  {
    result->type = jbvBool;
    result->val.boolean = false;
  }
  else
  {
    Assert(JBE_ISCONTAINER(entry));
    result->type = jbvBinary;
    /* Remove alignment padding from data pointer and length */
    result->val.binary.data = (JsonbContainer *) (base_addr + INTALIGN(offset));
    result->val.binary.len = getJsonbLength(container, index) -
      (INTALIGN(offset) - offset);
  }
}

/*
 * Push JsonbValue into JsonbParseState.
 *
 * Used when parsing JSON tokens to form Jsonb, or when converting an in-memory
 * JsonbValue to a Jsonb.
 *
 * Initial state of *JsonbParseState is NULL, since it'll be allocated here
 * originally (caller will get JsonbParseState back by reference).
 *
 * Only sequential tokens pertaining to non-container types should pass a
 * JsonbValue.  There is one exception -- WJB_BEGIN_ARRAY callers may pass a
 * "raw scalar" pseudo array to append it - the actual scalar should be passed
 * next and it will be added as the only member of the array.
 *
 * Values of type jvbBinary, which are rolled up arrays and objects,
 * are unpacked before being added to the result.
 */
JsonbValue *
pushJsonbValue(JsonbParseState **pstate, JsonbIteratorToken seq,
         JsonbValue *jbval)
{
  JsonbIterator *it;
  JsonbValue *res = NULL;
  JsonbValue  v;
  JsonbIteratorToken tok;

  if (!jbval || (seq != WJB_ELEM && seq != WJB_VALUE) ||
    jbval->type != jbvBinary)
  {
    /* drop through */
    return pushJsonbValueScalar(pstate, seq, jbval);
  }

  /* unpack the binary and add each piece to the pstate */
  it = JsonbIteratorInit(jbval->val.binary.data);
  while ((tok = JsonbIteratorNext(&it, &v, false)) != WJB_DONE)
    res = pushJsonbValueScalar(pstate, tok,
                   tok < WJB_BEGIN_ARRAY ? &v : NULL);

  return res;
}

/*
 * Do the actual pushing, with only scalar or pseudo-scalar-array values
 * accepted.
 */
static JsonbValue *
pushJsonbValueScalar(JsonbParseState **pstate, JsonbIteratorToken seq,
           JsonbValue *scalarVal)
{
  JsonbValue *result = NULL;

  switch (seq)
  {
    case WJB_BEGIN_ARRAY:
      Assert(!scalarVal || scalarVal->val.array.rawScalar);
      *pstate = pushState(pstate);
      result = &(*pstate)->contVal;
      (*pstate)->contVal.type = jbvArray;
      (*pstate)->contVal.val.array.nElems = 0;
      (*pstate)->contVal.val.array.rawScalar = (scalarVal &&
                       scalarVal->val.array.rawScalar);
      if (scalarVal && scalarVal->val.array.nElems > 0)
      {
        /* Assume that this array is still really a scalar */
        Assert(scalarVal->type == jbvArray);
        (*pstate)->size = scalarVal->val.array.nElems;
      }
      else
      {
        (*pstate)->size = 4;
      }
      (*pstate)->contVal.val.array.elems = palloc(sizeof(JsonbValue) *
                            (*pstate)->size);
      break;
    case WJB_BEGIN_OBJECT:
      Assert(!scalarVal);
      *pstate = pushState(pstate);
      result = &(*pstate)->contVal;
      (*pstate)->contVal.type = jbvObject;
      (*pstate)->contVal.val.object.nPairs = 0;
      (*pstate)->size = 4;
      (*pstate)->contVal.val.object.pairs = palloc(sizeof(JsonbPair) *
                             (*pstate)->size);
      break;
    case WJB_KEY:
      Assert(scalarVal->type == jbvString);
      appendKey(*pstate, scalarVal);
      break;
    case WJB_VALUE:
      Assert(IsAJsonbScalar(scalarVal));
      appendValue(*pstate, scalarVal);
      break;
    case WJB_ELEM:
      Assert(IsAJsonbScalar(scalarVal));
      appendElement(*pstate, scalarVal);
      break;
    case WJB_END_OBJECT:
      uniqueifyJsonbObject(&(*pstate)->contVal);
      /* fall through! */
    case WJB_END_ARRAY:
      /* Steps here common to WJB_END_OBJECT case */
      Assert(!scalarVal);
      result = &(*pstate)->contVal;

      /*
       * Pop stack and push current array/object as value in parent
       * array/object
       */
      *pstate = (*pstate)->next;
      if (*pstate)
      {
        switch ((*pstate)->contVal.type)
        {
          case jbvArray:
            appendElement(*pstate, result);
            break;
          case jbvObject:
            appendValue(*pstate, result);
            break;
          default:
            elog(ERROR, "invalid jsonb container type");
        }
      }
      break;
    default:
      elog(ERROR, "unrecognized jsonb sequential processing token");
  }

  return result;
}

/*
 * pushJsonbValue() worker:  Iteration-like forming of Jsonb
 */
static JsonbParseState *
pushState(JsonbParseState **pstate)
{
  JsonbParseState *ns = palloc(sizeof(JsonbParseState));

  ns->next = *pstate;
  return ns;
}

/*
 * pushJsonbValue() worker:  Append a pair key to state when generating a Jsonb
 */
static void
appendKey(JsonbParseState *pstate, JsonbValue *string)
{
  JsonbValue *object = &pstate->contVal;

  Assert(object->type == jbvObject);
  Assert(string->type == jbvString);

  if (object->val.object.nPairs >= JSONB_MAX_PAIRS)
    ereport(ERROR,
        (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
         errmsg("number of jsonb object pairs exceeds the maximum allowed (%zu)",
            JSONB_MAX_PAIRS)));

  if (object->val.object.nPairs >= pstate->size)
  {
    pstate->size *= 2;
    object->val.object.pairs = repalloc(object->val.object.pairs,
                      sizeof(JsonbPair) * pstate->size);
  }

  object->val.object.pairs[object->val.object.nPairs].key = *string;
  object->val.object.pairs[object->val.object.nPairs].order = object->val.object.nPairs;
}

/*
 * pushJsonbValue() worker:  Append a pair value to state when generating a
 * Jsonb
 */
static void
appendValue(JsonbParseState *pstate, JsonbValue *scalarVal)
{
  JsonbValue *object = &pstate->contVal;

  Assert(object->type == jbvObject);

  object->val.object.pairs[object->val.object.nPairs++].value = *scalarVal;
}

/*
 * pushJsonbValue() worker:  Append an element to state when generating a Jsonb
 */
static void
appendElement(JsonbParseState *pstate, JsonbValue *scalarVal)
{
  JsonbValue *array = &pstate->contVal;

  Assert(array->type == jbvArray);

  if (array->val.array.nElems >= JSONB_MAX_ELEMS)
    ereport(ERROR,
        (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
         errmsg("number of jsonb array elements exceeds the maximum allowed (%zu)",
            JSONB_MAX_ELEMS)));

  if (array->val.array.nElems >= pstate->size)
  {
    pstate->size *= 2;
    array->val.array.elems = repalloc(array->val.array.elems,
                      sizeof(JsonbValue) * pstate->size);
  }

  array->val.array.elems[array->val.array.nElems++] = *scalarVal;
}

/*
 * Given a JsonbContainer, expand to JsonbIterator to iterate over items
 * fully expanded to in-memory representation for manipulation.
 *
 * See JsonbIteratorNext() for notes on memory management.
 */
JsonbIterator *
JsonbIteratorInit(JsonbContainer *container)
{
  return iteratorFromContainer(container, NULL);
}

/*
 * Get next JsonbValue while iterating
 *
 * Caller should initially pass their own, original iterator.  They may get
 * back a child iterator palloc()'d here instead.  The function can be relied
 * on to free those child iterators, lest the memory allocated for highly
 * nested objects become unreasonable, but only if callers don't end iteration
 * early (by breaking upon having found something in a search, for example).
 *
 * Callers in such a scenario, that are particularly sensitive to leaking
 * memory in a long-lived context may walk the ancestral tree from the final
 * iterator we left them with to its oldest ancestor, pfree()ing as they go.
 * They do not have to free any other memory previously allocated for iterators
 * but not accessible as direct ancestors of the iterator they're last passed
 * back.
 *
 * Returns "Jsonb sequential processing" token value.  Iterator "state"
 * reflects the current stage of the process in a less granular fashion, and is
 * mostly used here to track things internally with respect to particular
 * iterators.
 *
 * Clients of this function should not have to handle any jbvBinary values
 * (since recursive calls will deal with this), provided skipNested is false.
 * It is our job to expand the jbvBinary representation without bothering them
 * with it.  However, clients should not take it upon themselves to touch array
 * or Object element/pair buffers, since their element/pair pointers are
 * garbage.  Also, *val will not be set when returning WJB_END_ARRAY or
 * WJB_END_OBJECT, on the assumption that it's only useful to access values
 * when recursing in.
 */
JsonbIteratorToken
JsonbIteratorNext(JsonbIterator **it, JsonbValue *val, bool skipNested)
{
  if (*it == NULL)
    return WJB_DONE;

  /*
   * When stepping into a nested container, we jump back here to start
   * processing the child. We will not recurse further in one call, because
   * processing the child will always begin in JBI_ARRAY_START or
   * JBI_OBJECT_START state.
   */
recurse:
  switch ((*it)->state)
  {
    case JBI_ARRAY_START:
      /* Set v to array on first array call */
      val->type = jbvArray;
      val->val.array.nElems = (*it)->nElems;

      /*
       * v->val.array.elems is not actually set, because we aren't doing
       * a full conversion
       */
      val->val.array.rawScalar = (*it)->isScalar;
      (*it)->curIndex = 0;
      (*it)->curDataOffset = 0;
      (*it)->curValueOffset = 0;  /* not actually used */
      /* Set state for next call */
      (*it)->state = JBI_ARRAY_ELEM;
      return WJB_BEGIN_ARRAY;

    case JBI_ARRAY_ELEM:
      if ((*it)->curIndex >= (*it)->nElems)
      {
        /*
         * All elements within array already processed.  Report this
         * to caller, and give it back original parent iterator (which
         * independently tracks iteration progress at its level of
         * nesting).
         */
        *it = freeAndGetParent(*it);
        return WJB_END_ARRAY;
      }

      fillJsonbValue((*it)->container, (*it)->curIndex,
               (*it)->dataProper, (*it)->curDataOffset,
               val);

      JBE_ADVANCE_OFFSET((*it)->curDataOffset,
                 (*it)->children[(*it)->curIndex]);
      (*it)->curIndex++;

      if (!IsAJsonbScalar(val) && !skipNested)
      {
        /* Recurse into container. */
        *it = iteratorFromContainer(val->val.binary.data, *it);
        goto recurse;
      }
      else
      {
        /*
         * Scalar item in array, or a container and caller didn't want
         * us to recurse into it.
         */
        return WJB_ELEM;
      }

    case JBI_OBJECT_START:
      /* Set v to object on first object call */
      val->type = jbvObject;
      val->val.object.nPairs = (*it)->nElems;

      /*
       * v->val.object.pairs is not actually set, because we aren't
       * doing a full conversion
       */
      (*it)->curIndex = 0;
      (*it)->curDataOffset = 0;
      (*it)->curValueOffset = getJsonbOffset((*it)->container,
                           (*it)->nElems);
      /* Set state for next call */
      (*it)->state = JBI_OBJECT_KEY;
      return WJB_BEGIN_OBJECT;

    case JBI_OBJECT_KEY:
      if ((*it)->curIndex >= (*it)->nElems)
      {
        /*
         * All pairs within object already processed.  Report this to
         * caller, and give it back original containing iterator
         * (which independently tracks iteration progress at its level
         * of nesting).
         */
        *it = freeAndGetParent(*it);
        return WJB_END_OBJECT;
      }
      else
      {
        /* Return key of a key/value pair.  */
        fillJsonbValue((*it)->container, (*it)->curIndex,
                 (*it)->dataProper, (*it)->curDataOffset,
                 val);
        if (val->type != jbvString)
          elog(ERROR, "unexpected jsonb type as object key");

        /* Set state for next call */
        (*it)->state = JBI_OBJECT_VALUE;
        return WJB_KEY;
      }

    case JBI_OBJECT_VALUE:
      /* Set state for next call */
      (*it)->state = JBI_OBJECT_KEY;

      fillJsonbValue((*it)->container, (*it)->curIndex + (*it)->nElems,
               (*it)->dataProper, (*it)->curValueOffset,
               val);

      JBE_ADVANCE_OFFSET((*it)->curDataOffset,
                 (*it)->children[(*it)->curIndex]);
      JBE_ADVANCE_OFFSET((*it)->curValueOffset,
               (*it)->children[(*it)->curIndex + (*it)->nElems]);
      (*it)->curIndex++;

      /*
       * Value may be a container, in which case we recurse with new,
       * child iterator (unless the caller asked not to, by passing
       * skipNested).
       */
      if (!IsAJsonbScalar(val) && !skipNested)
      {
        *it = iteratorFromContainer(val->val.binary.data, *it);
        goto recurse;
      }
      else
        return WJB_VALUE;
  }

  elog(ERROR, "invalid iterator state");
  return -1;
}

/*
 * Initialize an iterator for iterating all elements in a container.
 */
static JsonbIterator *
iteratorFromContainer(JsonbContainer *container, JsonbIterator *parent)
{
  JsonbIterator *it;

  it = palloc(sizeof(JsonbIterator));
  it->container = container;
  it->parent = parent;
  it->nElems = container->header & JB_CMASK;

  /* Array starts just after header */
  it->children = container->children;

  switch (container->header & (JB_FARRAY | JB_FOBJECT))
  {
    case JB_FARRAY:
      it->dataProper =
        (char *) it->children + it->nElems * sizeof(JEntry);
      it->isScalar = (container->header & JB_FSCALAR) != 0;
      /* This is either a "raw scalar", or an array */
      Assert(!it->isScalar || it->nElems == 1);

      it->state = JBI_ARRAY_START;
      break;

    case JB_FOBJECT:
      it->dataProper =
        (char *) it->children + it->nElems * sizeof(JEntry) * 2;
      it->state = JBI_OBJECT_START;
      break;

    default:
      elog(ERROR, "unknown type of jsonb container");
  }

  return it;
}

/*
 * JsonbIteratorNext() worker:  Return parent, while freeing memory for current
 * iterator
 */
static JsonbIterator *
freeAndGetParent(JsonbIterator *it)
{
  JsonbIterator *v = it->parent;

  pfree(it);
  return v;
}

/*
 * Worker for "contains" operator's function
 *
 * Formally speaking, containment is top-down, unordered subtree isomorphism.
 *
 * Takes iterators that belong to some container type.  These iterators
 * "belong" to those values in the sense that they've just been initialized in
 * respect of them by the caller (perhaps in a nested fashion).
 *
 * "val" is lhs Jsonb, and mContained is rhs Jsonb when called from top level.
 * We determine if mContained is contained within val.
 */
bool
JsonbDeepContains(JsonbIterator **val, JsonbIterator **mContained)
{
  JsonbValue  vval,
        vcontained;
  JsonbIteratorToken rval,
        rcont;

  /*
   * Guard against stack overflow due to overly complex Jsonb.
   *
   * Functions called here independently take this precaution, but that
   * might not be sufficient since this is also a recursive function.
   */
  check_stack_depth();

  rval = JsonbIteratorNext(val, &vval, false);
  rcont = JsonbIteratorNext(mContained, &vcontained, false);

  if (rval != rcont)
  {
    /*
     * The differing return values can immediately be taken as indicating
     * two differing container types at this nesting level, which is
     * sufficient reason to give up entirely (but it should be the case
     * that they're both some container type).
     */
    Assert(rval == WJB_BEGIN_OBJECT || rval == WJB_BEGIN_ARRAY);
    Assert(rcont == WJB_BEGIN_OBJECT || rcont == WJB_BEGIN_ARRAY);
    return false;
  }
  else if (rcont == WJB_BEGIN_OBJECT)
  {
    Assert(vval.type == jbvObject);
    Assert(vcontained.type == jbvObject);

    /*
     * If the lhs has fewer pairs than the rhs, it can't possibly contain
     * the rhs.  (This conclusion is safe only because we de-duplicate
     * keys in all Jsonb objects; thus there can be no corresponding
     * optimization in the array case.)  The case probably won't arise
     * often, but since it's such a cheap check we may as well make it.
     */
    if (vval.val.object.nPairs < vcontained.val.object.nPairs)
      return false;

    /* Work through rhs "is it contained within?" object */
    for (;;)
    {
      JsonbValue *lhsVal; /* lhsVal is from pair in lhs object */

      rcont = JsonbIteratorNext(mContained, &vcontained, false);

      /*
       * When we get through caller's rhs "is it contained within?"
       * object without failing to find one of its values, it's
       * contained.
       */
      if (rcont == WJB_END_OBJECT)
        return true;

      Assert(rcont == WJB_KEY);

      /* First, find value by key... */
      lhsVal = findJsonbValueFromContainer((*val)->container,
                         JB_FOBJECT,
                         &vcontained);

      if (!lhsVal)
        return false;

      /*
       * ...at this stage it is apparent that there is at least a key
       * match for this rhs pair.
       */
      rcont = JsonbIteratorNext(mContained, &vcontained, true);

      Assert(rcont == WJB_VALUE);

      /*
       * Compare rhs pair's value with lhs pair's value just found using
       * key
       */
      if (lhsVal->type != vcontained.type)
      {
        return false;
      }
      else if (IsAJsonbScalar(lhsVal))
      {
        if (!equalsJsonbScalarValue(lhsVal, &vcontained))
          return false;
      }
      else
      {
        /* Nested container value (object or array) */
        JsonbIterator *nestval,
               *nestContained;

        Assert(lhsVal->type == jbvBinary);
        Assert(vcontained.type == jbvBinary);

        nestval = JsonbIteratorInit(lhsVal->val.binary.data);
        nestContained = JsonbIteratorInit(vcontained.val.binary.data);

        /*
         * Match "value" side of rhs datum object's pair recursively.
         * It's a nested structure.
         *
         * Note that nesting still has to "match up" at the right
         * nesting sub-levels.  However, there need only be zero or
         * more matching pairs (or elements) at each nesting level
         * (provided the *rhs* pairs/elements *all* match on each
         * level), which enables searching nested structures for a
         * single String or other primitive type sub-datum quite
         * effectively (provided the user constructed the rhs nested
         * structure such that we "know where to look").
         *
         * In other words, the mapping of container nodes in the rhs
         * "vcontained" Jsonb to internal nodes on the lhs is
         * injective, and parent-child edges on the rhs must be mapped
         * to parent-child edges on the lhs to satisfy the condition
         * of containment (plus of course the mapped nodes must be
         * equal).
         */
        if (!JsonbDeepContains(&nestval, &nestContained))
          return false;
      }
    }
  }
  else if (rcont == WJB_BEGIN_ARRAY)
  {
    JsonbValue *lhsConts = NULL;
    uint32    nLhsElems = vval.val.array.nElems;

    Assert(vval.type == jbvArray);
    Assert(vcontained.type == jbvArray);

    /*
     * Handle distinction between "raw scalar" pseudo arrays, and real
     * arrays.
     *
     * A raw scalar may contain another raw scalar, and an array may
     * contain a raw scalar, but a raw scalar may not contain an array. We
     * don't do something like this for the object case, since objects can
     * only contain pairs, never raw scalars (a pair is represented by an
     * rhs object argument with a single contained pair).
     */
    if (vval.val.array.rawScalar && !vcontained.val.array.rawScalar)
      return false;

    /* Work through rhs "is it contained within?" array */
    for (;;)
    {
      rcont = JsonbIteratorNext(mContained, &vcontained, true);

      /*
       * When we get through caller's rhs "is it contained within?"
       * array without failing to find one of its values, it's
       * contained.
       */
      if (rcont == WJB_END_ARRAY)
        return true;

      Assert(rcont == WJB_ELEM);

      if (IsAJsonbScalar(&vcontained))
      {
        if (!findJsonbValueFromContainer((*val)->container,
                         JB_FARRAY,
                         &vcontained))
          return false;
      }
      else
      {
        uint32    i;

        /*
         * If this is first container found in rhs array (at this
         * depth), initialize temp lhs array of containers
         */
        if (lhsConts == NULL)
        {
          uint32    j = 0;

          /* Make room for all possible values */
          lhsConts = palloc(sizeof(JsonbValue) * nLhsElems);

          for (i = 0; i < nLhsElems; i++)
          {
            /* Store all lhs elements in temp array */
            rcont = JsonbIteratorNext(val, &vval, true);
            Assert(rcont == WJB_ELEM);

            if (vval.type == jbvBinary)
              lhsConts[j++] = vval;
          }

          /* No container elements in temp array, so give up now */
          if (j == 0)
            return false;

          /* We may have only partially filled array */
          nLhsElems = j;
        }

        /* XXX: Nested array containment is O(N^2) */
        for (i = 0; i < nLhsElems; i++)
        {
          /* Nested container value (object or array) */
          JsonbIterator *nestval,
                 *nestContained;
          bool    contains;

          nestval = JsonbIteratorInit(lhsConts[i].val.binary.data);
          nestContained = JsonbIteratorInit(vcontained.val.binary.data);

          contains = JsonbDeepContains(&nestval, &nestContained);

          if (nestval)
            pfree(nestval);
          if (nestContained)
            pfree(nestContained);
          if (contains)
            break;
        }

        /*
         * Report rhs container value is not contained if couldn't
         * match rhs container to *some* lhs cont
         */
        if (i == nLhsElems)
          return false;
      }
    }
  }
  else
  {
    elog(ERROR, "invalid jsonb container type");
  }

  elog(ERROR, "unexpectedly fell off end of jsonb container");
  return false;
}

/*
 * Hash a JsonbValue scalar value, mixing the hash value into an existing
 * hash provided by the caller.
 *
 * Some callers may wish to independently XOR in JB_FOBJECT and JB_FARRAY
 * flags.
 */
void
JsonbHashScalarValue(const JsonbValue *scalarVal, uint32 *hash)
{
  uint32    tmp;

  /* Compute hash value for scalarVal */
  switch (scalarVal->type)
  {
    case jbvNull:
      tmp = 0x01;
      break;
    case jbvString:
      tmp = DatumGetUInt32(hash_any((const unsigned char *) scalarVal->val.string.val,
                      scalarVal->val.string.len));
      break;
    case jbvNumeric:
      /* Must hash equal numerics to equal hash codes */
      tmp = DatumGetUInt32(DirectFunctionCall1(hash_numeric,
                   NumericGetDatum(scalarVal->val.numeric)));
      break;
    case jbvBool:
      tmp = scalarVal->val.boolean ? 0x02 : 0x04;

      break;
    default:
      elog(ERROR, "invalid jsonb scalar type");
      tmp = 0;      /* keep compiler quiet */
      break;
  }

  /*
   * Combine hash values of successive keys, values and elements by rotating
   * the previous value left 1 bit, then XOR'ing in the new
   * key/value/element's hash value.
   */
  *hash = (*hash << 1) | (*hash >> 31);
  *hash ^= tmp;
}

/*
 * Are two scalar JsonbValues of the same type a and b equal?
 */
static bool
equalsJsonbScalarValue(JsonbValue *aScalar, JsonbValue *bScalar)
{
  if (aScalar->type == bScalar->type)
  {
    switch (aScalar->type)
    {
      case jbvNull:
        return true;
      case jbvString:
        return lengthCompareJsonbStringValue(aScalar, bScalar) == 0;
      case jbvNumeric:
        return DatumGetBool(DirectFunctionCall2(numeric_eq,
                     PointerGetDatum(aScalar->val.numeric),
                   PointerGetDatum(bScalar->val.numeric)));
      case jbvBool:
        return aScalar->val.boolean == bScalar->val.boolean;

      default:
        elog(ERROR, "invalid jsonb scalar type");
    }
  }
  elog(ERROR, "jsonb scalar type mismatch");
  return -1;
}

/*
 * Compare two scalar JsonbValues, returning -1, 0, or 1.
 *
 * Strings are compared using the default collation.  Used by B-tree
 * operators, where a lexical sort order is generally expected.
 */
static int
compareJsonbScalarValue(JsonbValue *aScalar, JsonbValue *bScalar)
{
  if (aScalar->type == bScalar->type)
  {
    switch (aScalar->type)
    {
      case jbvNull:
        return 0;
      case jbvString:
        return varstr_cmp(aScalar->val.string.val,
                  aScalar->val.string.len,
                  bScalar->val.string.val,
                  bScalar->val.string.len);
      case jbvNumeric:
        return DatumGetInt32(DirectFunctionCall2(numeric_cmp,
                     PointerGetDatum(aScalar->val.numeric),
                   PointerGetDatum(bScalar->val.numeric)));
      case jbvBool:
        if (aScalar->val.boolean == bScalar->val.boolean)
          return 0;
        else if (aScalar->val.boolean >bScalar->val.boolean)
          return 1;
        else
          return -1;
      default:
        elog(ERROR, "invalid jsonb scalar type");
    }
  }
  elog(ERROR, "jsonb scalar type mismatch");
  return -1;
}


/*
 * Functions for manipulating the resizeable buffer used by convertJsonb and
 * its subroutines.
 */

/*
 * Reserve 'len' bytes, at the end of the buffer, enlarging it if necessary.
 * Returns the offset to the reserved area. The caller is expected to fill
 * the reserved area later with copyToBuffer().
 */
static int
reserveFromBuffer(StringInfo buffer, int len)
{
  int     offset;

  /* Make more room if needed */
  enlargeStringInfo(buffer, len);

  /* remember current offset */
  offset = buffer->len;

  /* reserve the space */
  buffer->len += len;

  /*
   * Keep a trailing null in place, even though it's not useful for us; it
   * seems best to preserve the invariants of StringInfos.
   */
  buffer->data[buffer->len] = '\0';

  return offset;
}

/*
 * Copy 'len' bytes to a previously reserved area in buffer.
 */
static void
copyToBuffer(StringInfo buffer, int offset, const char *data, int len)
{
  memcpy(buffer->data + offset, data, len);
}

/*
 * A shorthand for reserveFromBuffer + copyToBuffer.
 */
static void
appendToBuffer(StringInfo buffer, const char *data, int len)
{
  int     offset;

  offset = reserveFromBuffer(buffer, len);
  copyToBuffer(buffer, offset, data, len);
}


/*
 * Append padding, so that the length of the StringInfo is int-aligned.
 * Returns the number of padding bytes appended.
 */
static short
padBufferToInt(StringInfo buffer)
{
  int     padlen,
        p,
        offset;

  padlen = INTALIGN(buffer->len) - buffer->len;

  offset = reserveFromBuffer(buffer, padlen);

  /* padlen must be small, so this is probably faster than a memset */
  for (p = 0; p < padlen; p++)
    buffer->data[offset + p] = '\0';

  return padlen;
}

/*
 * Given a JsonbValue, convert to Jsonb. The result is palloc'd.
 */
static Jsonb *
convertToJsonb(JsonbValue *val)
{
  StringInfoData buffer;
  JEntry    jentry;
  Jsonb    *res;

  /* Should not already have binary representation */
  Assert(val->type != jbvBinary);

  /* Allocate an output buffer. It will be enlarged as needed */
  initStringInfo(&buffer);

  /* Make room for the varlena header */
  reserveFromBuffer(&buffer, VARHDRSZ);

  convertJsonbValue(&buffer, &jentry, val, 0);

  /*
   * Note: the JEntry of the root is discarded. Therefore the root
   * JsonbContainer struct must contain enough information to tell what kind
   * of value it is.
   */

  res = (Jsonb *) buffer.data;

  SET_VARSIZE(res, buffer.len);

  return res;
}

/*
 * Subroutine of convertJsonb: serialize a single JsonbValue into buffer.
 *
 * The JEntry header for this node is returned in *header.  It is filled in
 * with the length of this value and appropriate type bits.  If we wish to
 * store an end offset rather than a length, it is the caller's responsibility
 * to adjust for that.
 *
 * If the value is an array or an object, this recurses. 'level' is only used
 * for debugging purposes.
 */
static void
convertJsonbValue(StringInfo buffer, JEntry *header, JsonbValue *val, int level)
{
  check_stack_depth();

  if (!val)
    return;

  /*
   * A JsonbValue passed as val should never have a type of jbvBinary, and
   * neither should any of its sub-components. Those values will be produced
   * by convertJsonbArray and convertJsonbObject, the results of which will
   * not be passed back to this function as an argument.
   */

  if (IsAJsonbScalar(val))
    convertJsonbScalar(buffer, header, val);
  else if (val->type == jbvArray)
    convertJsonbArray(buffer, header, val, level);
  else if (val->type == jbvObject)
    convertJsonbObject(buffer, header, val, level);
  else
    elog(ERROR, "unknown type of jsonb container to convert");
}

static void
convertJsonbArray(StringInfo buffer, JEntry *pheader, JsonbValue *val, int level)
{
  int     base_offset;
  int     jentry_offset;
  int     i;
  int     totallen;
  uint32    header;
  int     nElems = val->val.array.nElems;

  /* Remember where in the buffer this array starts. */
  base_offset = buffer->len;

  /* Align to 4-byte boundary (any padding counts as part of my data) */
  padBufferToInt(buffer);

  /*
   * Construct the header Jentry and store it in the beginning of the
   * variable-length payload.
   */
  header = nElems | JB_FARRAY;
  if (val->val.array.rawScalar)
  {
    Assert(nElems == 1);
    Assert(level == 0);
    header |= JB_FSCALAR;
  }

  appendToBuffer(buffer, (char *) &header, sizeof(uint32));

  /* Reserve space for the JEntries of the elements. */
  jentry_offset = reserveFromBuffer(buffer, sizeof(JEntry) * nElems);

  totallen = 0;
  for (i = 0; i < nElems; i++)
  {
    JsonbValue *elem = &val->val.array.elems[i];
    int     len;
    JEntry    meta;

    /*
     * Convert element, producing a JEntry and appending its
     * variable-length data to buffer
     */
    convertJsonbValue(buffer, &meta, elem, level + 1);

    len = JBE_OFFLENFLD(meta);
    totallen += len;

    /*
     * Bail out if total variable-length data exceeds what will fit in a
     * JEntry length field.  We check this in each iteration, not just
     * once at the end, to forestall possible integer overflow.
     */
    if (totallen > JENTRY_OFFLENMASK)
      ereport(ERROR,
          (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
           errmsg("total size of jsonb array elements exceeds the maximum of %u bytes",
              JENTRY_OFFLENMASK)));

    /*
     * Convert each JB_OFFSET_STRIDE'th length to an offset.
     */
    if ((i % JB_OFFSET_STRIDE) == 0)
      meta = (meta & JENTRY_TYPEMASK) | totallen | JENTRY_HAS_OFF;

    copyToBuffer(buffer, jentry_offset, (char *) &meta, sizeof(JEntry));
    jentry_offset += sizeof(JEntry);
  }

  /* Total data size is everything we've appended to buffer */
  totallen = buffer->len - base_offset;

  /* Check length again, since we didn't include the metadata above */
  if (totallen > JENTRY_OFFLENMASK)
    ereport(ERROR,
        (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
         errmsg("total size of jsonb array elements exceeds the maximum of %u bytes",
            JENTRY_OFFLENMASK)));

  /* Initialize the header of this node in the container's JEntry array */
  *pheader = JENTRY_ISCONTAINER | totallen;
}

static void
convertJsonbObject(StringInfo buffer, JEntry *pheader, JsonbValue *val, int level)
{
  int     base_offset;
  int     jentry_offset;
  int     i;
  int     totallen;
  uint32    header;
  int     nPairs = val->val.object.nPairs;

  /* Remember where in the buffer this object starts. */
  base_offset = buffer->len;

  /* Align to 4-byte boundary (any padding counts as part of my data) */
  padBufferToInt(buffer);

  /*
   * Construct the header Jentry and store it in the beginning of the
   * variable-length payload.
   */
  header = nPairs | JB_FOBJECT;
  appendToBuffer(buffer, (char *) &header, sizeof(uint32));

  /* Reserve space for the JEntries of the keys and values. */
  jentry_offset = reserveFromBuffer(buffer, sizeof(JEntry) * nPairs * 2);

  /*
   * Iterate over the keys, then over the values, since that is the ordering
   * we want in the on-disk representation.
   */
  totallen = 0;
  for (i = 0; i < nPairs; i++)
  {
    JsonbPair  *pair = &val->val.object.pairs[i];
    int     len;
    JEntry    meta;

    /*
     * Convert key, producing a JEntry and appending its variable-length
     * data to buffer
     */
    convertJsonbScalar(buffer, &meta, &pair->key);

    len = JBE_OFFLENFLD(meta);
    totallen += len;

    /*
     * Bail out if total variable-length data exceeds what will fit in a
     * JEntry length field.  We check this in each iteration, not just
     * once at the end, to forestall possible integer overflow.
     */
    if (totallen > JENTRY_OFFLENMASK)
      ereport(ERROR,
          (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
           errmsg("total size of jsonb object elements exceeds the maximum of %u bytes",
              JENTRY_OFFLENMASK)));

    /*
     * Convert each JB_OFFSET_STRIDE'th length to an offset.
     */
    if ((i % JB_OFFSET_STRIDE) == 0)
      meta = (meta & JENTRY_TYPEMASK) | totallen | JENTRY_HAS_OFF;

    copyToBuffer(buffer, jentry_offset, (char *) &meta, sizeof(JEntry));
    jentry_offset += sizeof(JEntry);
  }
  for (i = 0; i < nPairs; i++)
  {
    JsonbPair  *pair = &val->val.object.pairs[i];
    int     len;
    JEntry    meta;

    /*
     * Convert value, producing a JEntry and appending its variable-length
     * data to buffer
     */
    convertJsonbValue(buffer, &meta, &pair->value, level + 1);

    len = JBE_OFFLENFLD(meta);
    totallen += len;

    /*
     * Bail out if total variable-length data exceeds what will fit in a
     * JEntry length field.  We check this in each iteration, not just
     * once at the end, to forestall possible integer overflow.
     */
    if (totallen > JENTRY_OFFLENMASK)
      ereport(ERROR,
          (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
           errmsg("total size of jsonb object elements exceeds the maximum of %u bytes",
              JENTRY_OFFLENMASK)));

    /*
     * Convert each JB_OFFSET_STRIDE'th length to an offset.
     */
    if (((i + nPairs) % JB_OFFSET_STRIDE) == 0)
      meta = (meta & JENTRY_TYPEMASK) | totallen | JENTRY_HAS_OFF;

    copyToBuffer(buffer, jentry_offset, (char *) &meta, sizeof(JEntry));
    jentry_offset += sizeof(JEntry);
  }

  /* Total data size is everything we've appended to buffer */
  totallen = buffer->len - base_offset;

  /* Check length again, since we didn't include the metadata above */
  if (totallen > JENTRY_OFFLENMASK)
    ereport(ERROR,
        (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
         errmsg("total size of jsonb object elements exceeds the maximum of %u bytes",
            JENTRY_OFFLENMASK)));

  /* Initialize the header of this node in the container's JEntry array */
  *pheader = JENTRY_ISCONTAINER | totallen;
}

static void
convertJsonbScalar(StringInfo buffer, JEntry *jentry, JsonbValue *scalarVal)
{
  int     numlen;
  short   padlen;

  switch (scalarVal->type)
  {
    case jbvNull:
      *jentry = JENTRY_ISNULL;
      break;

    case jbvString:
      appendToBuffer(buffer, scalarVal->val.string.val, scalarVal->val.string.len);

      *jentry = scalarVal->val.string.len;
      break;

    case jbvNumeric:
      numlen = VARSIZE_ANY(scalarVal->val.numeric);
      padlen = padBufferToInt(buffer);

      appendToBuffer(buffer, (char *) scalarVal->val.numeric, numlen);

      *jentry = JENTRY_ISNUMERIC | (padlen + numlen);
      break;

    case jbvBool:
      *jentry = (scalarVal->val.boolean) ?
        JENTRY_ISBOOL_TRUE : JENTRY_ISBOOL_FALSE;
      break;

    default:
      elog(ERROR, "invalid jsonb scalar type");
  }
}

/*
 * Compare two jbvString JsonbValue values, a and b.
 *
 * This is a special qsort() comparator used to sort strings in certain
 * internal contexts where it is sufficient to have a well-defined sort order.
 * In particular, object pair keys are sorted according to this criteria to
 * facilitate cheap binary searches where we don't care about lexical sort
 * order.
 *
 * a and b are first sorted based on their length.  If a tie-breaker is
 * required, only then do we consider string binary equality.
 */
static int
lengthCompareJsonbStringValue(const void *a, const void *b)
{
  const JsonbValue *va = (const JsonbValue *) a;
  const JsonbValue *vb = (const JsonbValue *) b;
  int     res;

  Assert(va->type == jbvString);
  Assert(vb->type == jbvString);

  if (va->val.string.len == vb->val.string.len)
  {
    res = memcmp(va->val.string.val, vb->val.string.val, va->val.string.len);
  }
  else
  {
    res = (va->val.string.len > vb->val.string.len) ? 1 : -1;
  }

  return res;
}

/*
 * qsort_arg() comparator to compare JsonbPair values.
 *
 * Third argument 'binequal' may point to a bool. If it's set, *binequal is set
 * to true iff a and b have full binary equality, since some callers have an
 * interest in whether the two values are equal or merely equivalent.
 *
 * N.B: String comparisons here are "length-wise"
 *
 * Pairs with equals keys are ordered such that the order field is respected.
 */
static int
lengthCompareJsonbPair(const void *a, const void *b, void *binequal)
{
  const JsonbPair *pa = (const JsonbPair *) a;
  const JsonbPair *pb = (const JsonbPair *) b;
  int     res;

  res = lengthCompareJsonbStringValue(&pa->key, &pb->key);
  if (res == 0 && binequal)
    *((bool *) binequal) = true;

  /*
   * Guarantee keeping order of equal pair.  Unique algorithm will prefer
   * first element as value.
   */
  if (res == 0)
    res = (pa->order > pb->order) ? -1 : 1;

  return res;
}

/*
 * Sort and unique-ify pairs in JsonbValue object
 */
static void
uniqueifyJsonbObject(JsonbValue *object)
{
  bool    hasNonUniq = false;

  Assert(object->type == jbvObject);

  if (object->val.object.nPairs > 1)
    qsort_arg(object->val.object.pairs, object->val.object.nPairs, sizeof(JsonbPair),
          lengthCompareJsonbPair, &hasNonUniq);

  if (hasNonUniq)
  {
    JsonbPair  *ptr = object->val.object.pairs + 1,
           *res = object->val.object.pairs;

    while (ptr - object->val.object.pairs < object->val.object.nPairs)
    {
      /* Avoid copying over duplicate */
      if (lengthCompareJsonbStringValue(ptr, res) != 0)
      {
        res++;
        if (ptr != res)
          memcpy(res, ptr, sizeof(JsonbPair));
      }
      ptr++;
    }

    object->val.object.nPairs = res + 1 - object->val.object.pairs;
  }
}
